A: Depending on the size of the hot tub, the amount of water it holds, and the type of heater installed in the spa, this time will vary. However, it is important to know that above ground portable spas with electric heaters do not heat quickly, as many gas-heated gunite spas will. On average, a spa will heat about 5 - 7 degrees Fahrenheit per hour using a 6kw heater on 240V.
